1. Field of the Invention
This invention relates in general to the construction of an apparatus for accurately measuring the force required to crush particles of solid material such as contact catalysts, adsorbents, and other particulate solid material. In particular it relates to a new and useful construction for a machine operating on the law of levers whereby a rolling weight applies a gradually increasing and measurable and controlled crushing force to a solid particle.
2. Description of Prior Art
Devices for the measurement of the force required to crush solid particles are widely used in industrial laboratories. Such measurements are called crush tests. The maximum force produced by a dead weight load that a particle can support without losing its integrity is called its crush strength. The figure is useful in predicting whether solid particles arranged in a fixed bed reactor or adsorber will collapse and attrit to a powder during use.
Several methods and devices are available for measuring particle crush strength. In some, a particle is placed between a base and a piston driven from a hydraulic cylinder. Fluid pressure in the cylinder is increased until the particle collapses. Its crush strength is measured from the known cylinder pressure and total force on the piston caused by that pressure. Air or water or oil have been used as the pressurizing fluid in such devices.
In another type of device a spring force is used instead of hydraulic force. An anvil is pressed against the particle by means of a spring. The force on the particle at the instant it collapses is measured and computed from the measured spring length at the instant of particle collapse.
In most available methods the particle can be placed on a base and the crushing force applied vertically downward, or the particle can be pushed against a retaining wall and the force applied laterally.
Disadvantages of the commercially applied methods are the inaccuracies introduced by such things as erroneous or inoperative pressure gauges, errors in knowing the correct value of the spring constant or even having a spring in the apparatus which is different from the one that is thought to be there. Furthermore, different calibration curves are needed from time to time to convert spring elongations or pressure guage readings into crushing force. Unless special means are incorporated into such devices, the rate at which load is applied to the particle is generally not known even though such rate of application has a profound effect on the ultimate crush strength of the particle.
A very crude particle crush tester is a hand nutcracker of the type where the nut to be cracked is placed between two hinged members. The members are then squeezed together by hand to crack the nut. The problem with this type of crush tester is that measurement of crush strength is inaccurate since it depends on the personal judgement as to what position along the members it was held, where the nut was actually located and how hard and how fast it was squeezed. In the subject invention a way has been discovered to simply quantify such a nutcracker principle and thereby produce a very simple and vastly superior crush strength tester.